[SI-LIST] Re: AW: AW: When a signal is considered high speed signal
- From: Praveen Gowda <praveenkumardr@xxxxxxxxx>
- To: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- Date: Wed, 23 Sep 2009 16:19:32 +0530
Can any one, send the link for John A. DeFalco's, paper, "Predicting
Crosstalk in Digital Systems," *Computer Design*, June 1973
If the document is in IEEE, please send the link..
On Tue, Sep 22, 2009 at 1:07 PM, Havermann, Gert <Gert.Havermann@xxxxxxxxxxx
> wrote:
> Lee,
>
> you are right, designing for high speed according the signals risetime is
> the best way, but especially for lower signal speeds, you can easily run
> into SI problems even when designing for high speeds. For example, some
> connectors (D-Sub, RJ45...) along the signal path might be well suited for
> the desired signal speed, but show very high impedance mismatch at higher
> frequencies. If you like to keep those components, you have to get rid of
> the high frequency content.
> Adding capacitance can cause PDS problems. According to Murphy, the small
> tricks solve one problem and cause another. We did this successfully in many
> designs, especially when the chip manufacturer changed the chip to a smaller
> die size. Chip manufacturers often claim that the function is identical,
> just the size is different, but we all know, that shrinking the die causes
> faster risetimes.
> In cases where a capacitor did not work, we used smaller and longer traces
> to add loss. This might not be an option for a small board, but it works
> very well.
>
> BR
> Gert
>
>
> --------------------------------------------------------------------------
> Absender ist HARTING Electronics GmbH & Co. KG; Sitz der Gesellschaft:
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> persönlich haftende Gesellschafterin: HARTING Electronics Management GmbH;
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> 8808; Geschäftsführer: Torsten Ratzmann
> -----Ursprüngliche Nachricht-----
>
> Von: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx]
> Gesendet: Montag, 21. September 2009 22:24
> An: Havermann, Gert; si-list@xxxxxxxxxxxxx
> Betreff: RE: [SI-LIST] AW: When a signal is considered high speed signal
>
> Gert,
>
> Adding capacitance on an output to slow it down solved the rise time
> problem. However, this had an adverse affect on the PDS as there will be a
> larger current drawn from it when the signal goes from 0 to 1 to charge up
> this capacitor. If I can't get the IC manufacturer to slow down the edges,
> I just treat the signal like a hig hspeed signal, even when it is supposed
> to run slow.
>
> Lee
>
>
> > [Original Message]
> > From: Havermann, Gert <Gert.Havermann@xxxxxxxxxxx>
> > To: <si-list@xxxxxxxxxxxxx>
> > Date: 9/21/2009 4:50:39 AM
> > Subject: [SI-LIST] AW: When a signal is considered high speed signal
> >
> > Hi Rama,
> >
> > I'd like to add an info to the definition in Lee Ritcheys first book.
> > Due to the trend to smaller Die sizes, risetimes become much faster
> > than
> needed for the desired signal speeds. This is the reason, why a some
> designs have "high speed issues" in the Mb range already. You should always
> look at the desired risetime. If the chips risetime is much higher than
> needed, one should consider to add capacitance to get rid of the unwanted
> high frequency content of the signal.
> >
> > I would put it this way: a signal is considered high speed when the
> tracelength exceeds 1/4TEL based on the "needed" risetime.
> >
> > BR
> > Gert
> >
> >
> > ----------------------------------------------------------------------
> > ---- Absender ist HARTING Electronics GmbH & Co. KG; Sitz der
> > Gesellschaft:
> Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596;
> persönlich haftende Gesellschafterin: HARTING Electronics Management GmbH;
> Sitz der Komplementär-GmbH: Espelkamp; Registergericht der
> Komplementär-GmbH: Bad Oeynhausen; Register-Nr. der Komplementär-GmbH:
> HRB 8808; Geschäftsführer: Torsten Ratzmann
> > -----Ursprüngliche Nachricht-----
> >
> > Von: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]
> Im Auftrag von Rama Mohan Reddy Boreddy
> > Gesendet: Montag, 21. September 2009 08:52
> > An: si-list@xxxxxxxxxxxxx
> > Betreff: [SI-LIST] When a signal is considered high speed signal
> >
> > Hi,
> > Can anyone tell when a signal is considered as a high speed signal?
> Is there any definition for high speed signal in time domain and frequency
> domain?
> >
> > I know that a rise time and PCB trace/Interconnect legth is one of
> the parameters to define a signal as high speed signal. Can any body
> provide me the formula
> >
> > Can any body share a FAQ on high speed signals and Cross talk
> >
> > Regards,
> > Rama Mohan Reddy
> >
> >
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